The SOPHIA Monte Carlo Code

Pionphot 1Pionphot 2

Monte Carlo simulations of photohadronic processes in astrophysics

Computer Physics Communications, 124, 290-314 

The cosmic ray spectrum extends to extremely high energies. Giant air showers have been observed with energy exceeding ~1011 GeV. Energy losses due to interactions with ambient photons can become important, even dominant for such energetic nucleons, above the threshold for pion production. Photoproduction of hadrons is expected to cause a distortion of the ultra-high energy cosmic ray (CR) spectrum by interactions of the nucleons with the microwave background (the Greisen-Zatsepin-Kuzmin cutoff), but it may also be relevant to the observed high energy gamma ray emission from jets of Active Galactic Nuclei (AGN) or Gamma-Ray Bursts (GRB). Moreover, it is the major source process for the predicted fluxes of very high energy cosmic neutrinos.

The photohadronic cross section at low interaction energies is dominated by the Delta(1232) resonance. Since the low energy region of the cross section is emphasized in many astrophysical applications, the cross section and decay properties of the prominent Delta-resonance have often been used as an approximation for photopion production, and the subsequent production of gamma rays and neutrinos. As discussed in e.g. Mücke et al. 1999, this approximation is only valid for a restricted number of cases, and does not describe sufficiently well the whole energy range of photohadronic interactions. A more sophisticated photoproduction simulation code is needed to cover the center-of-mass energy range of about s1/2~1 - 103 GeV, which is important in many astrophysical applications.

This was the motivation for developing the Monte-Carlo event generator SOPHIA (Simulations Of Photo Hadronic Interactions in Astrophysics), which we wrote as a tool for solving problems connected to photohadronic processes in astrophysical environments, but can also be used for radiation and background studies at high energy colliders such as LEP2 and HERA, as well as for simulations of photon induced air showers. The philosophy of the development of SOPHIA has been to implement well established phenomenological models, symmetries of hadronic interactions in a way that describes correctly the available exclusive and inclusive photohadronic cross section data obtained at fixed target and collider experiments.

We plan to continue investigating a variety of astrophysics topics related to photomeson production using the SOPHIA code. Past studies by members of the SOPHIA collaboration include:


  • hadronic blazar emission models (Synchrotron-Proton blazar model)
  • cosmic ray propagation
  • ...

where the SOPHIA package has been used:

A. Mücke, Ralph Engel, J.P. Rachen, R.J. Protheroe, and Todor Stanev, 2000, Comp. Phys. Commun., 124, 290:
Monte Carlo simulations of photohadronic processes in astrophysics

A. Mücke & R.J. Protheroe, 2000, AIP, 515, 149:
Modeling the April 1997 Flare of Mkn 501

T. Stanev, R. Engel, A. Mücke, R.J. Protheroe, J.P. Rachen, 2000, Phys. Rev. D, 62, 093005:
Propagation of ultrahigh energy protons in the nearby universe

R.J. Protheroe & A. Mücke, 2001, AIP, 558, 700:
Application of the Synchrotron Proton Blazar Model to BL Lac Objects

R.J. Protheroe & A. Mücke, 2001, ASPC, 250, 113:
Estimating jet power in proton blazar models

A. Mücke & R.J. Protheroe, 2001, ICRC, 3, 1153:
Neutrino Emission from HBLs and LBLs

A. Mücke & R.J. Protheroe,2001, APh, 15, 121:
A proton synchrotron blazar model for flaring in Markarian 501

A. Mücke, R.J. Protheroe, R. Engel, J. Rachen, T. Stanev, 2003, APh, 18, 593:
BL Lac objects in the synchrotron proton blazar model